The present invention relates generally to wood preservative compositions, and more particularly to synergistic biocidal compositions that combine low cost copper salts and organic biocides to preserve wood.
Wood is an important building and construction material and its importance and use continues to increase. Examples of its uses include general construction, residential housing, utility poles, crossing arms, fence posts, railroad ties and pilings, etc. For its various uses, wood must be protected from attack by insects, fungi and other organisms. Insects, such as termites, beetles and carpenter ants, cause extensive and costly damage to wood structures. Wood-attacking fungi, such as brown-rot and white-rot, will structurally weaken wood by damaging the cellulose and lignin. If left unprotected or unpreserved, wood will decay and deteriorate within a period of a few months to a few years, depending upon climate and soil conditions. Wood objects such as utility poles and timbers will deteriorate rapidly below ground level and will require frequent replacement if not properly and adequately preserved by chemical preservative treatment.
Toxicity to various wood-attacking organisms is an essential requirement of wood preservatives. The preservative treatments for wood must effectively repel attacking organisms for an extended period, i.e., provide long lasting protection. In addition, wood preservatives should have favorable wood penetrating properties, should not corrode metals and should be safe to handle by those treating the wood and using the furnished wood product.
Through the years, a number of different compounds have been used for preserving wood. Among these compounds include creosote, heavy metal salts, heavy oils and tars, pitch and various organic chemicals. Each of these compounds has its advantages and drawbacks.
For instance, creosote, as well as other heavy oils, tars and pitch treatments, has a strong odor and leaves the surface greasy and oily to the touch making the treated wood more difficult to handle. Halogenated phenols are also widely used as commercial wood preservatives because they have good fungicidal and insecticidal properties. The halogenated phenols are dissolved in hydrocarbon solvents, such as medium aromatic oils, volatile petroleum solvents (propane), light solvents (mineral spirits), or in a chlorinated hydrocarbon solvent-inhibited grade of methylene chloride.
Pentachlorophenol is a commonly used phenol preservative due to its effectiveness, relative ease of application and durability. However, recent environmental concerns are expected to limit the use of pentachlorophenol in the future. Copper and other heavy metals are good biocides. However, copper is not effective as a wood preservative since it does not control Postia sp. and other fungi which are copper tolerant.
Wood preservatives can be applied to wood as solutions, emulsions, pastes or dispersions in liquid hydrocarbons and/or aqueous systems. Water-borne preservatives are usually less expensive. In many applications, the use of water-borne preservatives are preferred, because of the odors, flammability and often toxic nature of liquid hydrocarbon solvents.
The protection afforded by the application of any wood preservative is dependent upon the depth and uniformity of the penetration into the wood or timber. The treatment of wood material usually comprises soaking or impregnating the wood with the fluid-borne treating chemicals. Another technique that is practiced in a number of variants is the full-cell process, where the pores of the wood material are partially evacuated before impregnation in order to increase the fluid retained therein, or the empty-cell process which is similar to the full-cell process except that the preliminary step of evacuation is omitted.
The most common commercial procedures for impregnating wood involve contacting the wood with the preservative under a relatively high pressure, for example, 50-200 psi (pounds per square inch) for a period of time, such as from one-half hour to twenty four hours. The processing may also require relatively high temperatures in the range from about 75.degree. C. to about 105.degree. to 110.degree. C.
Upon contact and penetration into wood materials and during the drying process, the preservative in the wood preferably becomes fixed and essentially non-leachable. In various formulations, water in widely varying percentages is used as the main solvent for the treating solution.
In the course of treating wood with different biocides, certain insects and fungi are found not to be repelled by particular chemical treatments. In order to protect against a broader range of such insects and fungi, combinations of preservatives are sometimes used. Some combinations of preservatives have been found to have a greater effective than the sum of their individual components, and are considered synergistic.
An object of the present invention is to provide copper salt and organic preservative compositions that have synergistic effects in treating wood.
Another object of the present invention is to provide combinations of preservatives that are highly effective and less costly to use.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention.